Our overall goal is to define the properties of anti-viral CD8+ T cells that should be elicited by an efficacious HIV-1 vaccine. Indeed, an NIH-sponsored, phase IIb, proof-of-concept trial was initiated specifically to test whether a multi-clade Env+Gag prime-boost strategy elicits HIV-1 specific CD8+ T lymphocyte responses that can reduce viral load in those who become infected with HIV-1. Some aspects of CD8+ immune responses have been reproducibly associated with virus control. However, a recently completed HIV-1 vaccine trial elicited HIV-specific CD8 T cells with no effect on viral control. These studies underscore the critical need to evaluate surrogate markers of virus inhibitory CD8+ T cell responses in assessing vaccine efficacy. The precise mechanisms underpinning the ability of CD8+ T cells to inhibit virus replication must be defined in order to inform future trial design. We found that HIV-1 vaccination elicits CD8+ T cell mediated HIV-1 inhibition, and that CD107a and MIP-12 expression strongly associates with this antiviral CD8+ T cell response. Moreover, the antiviral CD8+ T cell response is modulated by epigenetic mechanisms, thereby providing a new paradigm for the induction of effective CD8+ T cell responses. This project builds significantly upon our recently published work using the innovative combined strategies of CD8+ T cell virus inhibition assays, multiparameter flow cytometry with cell sorting, and molecular techniques to interrogate gene expression to characterize anti-viral HIV-1-specific CD8+ T cells and define the mechanisms underlying that inhibition. We will examine the phenotype and function of CD8+ T cells in four unique cohorts including elite controllers and HIV-1 vaccinees. Completion of the project will provide key data that will enable optimization of vaccine regimens to elicit CD8+ T cells capable of suppressing HIV-1.